Apoptosis and recognition of apoptotic cells in colonial ascidians

Colonies of the compound ascidian Botryllus schlosseri undergo a cyclical generation change, known as take-over, during which cell death occurs and senescent cells are recognised and rapidly ingested by circulating phagocytes. We re-examined, by means of morphological and cytochemical approaches, the cell death process which occurs during take-over, focussing on circulating haemocytes as reference tissue. Since dying cells are actively ingested by circulating phagocytes, we studied the expression of phosphatidylserine and CD36 in senescent cells and phagocytes, respectively, and their role in the recognition of effete cells by phagocytes.